US20060197567A1 - DLL circuit for providing an adjustable phase relationship with respect to a periodic input signal - Google Patents
DLL circuit for providing an adjustable phase relationship with respect to a periodic input signal Download PDFInfo
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- US20060197567A1 US20060197567A1 US11/360,988 US36098806A US2006197567A1 US 20060197567 A1 US20060197567 A1 US 20060197567A1 US 36098806 A US36098806 A US 36098806A US 2006197567 A1 US2006197567 A1 US 2006197567A1
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/08—Details of the phase-locked loop
- H03L7/081—Details of the phase-locked loop provided with an additional controlled phase shifter
- H03L7/0812—Details of the phase-locked loop provided with an additional controlled phase shifter and where no voltage or current controlled oscillator is used
- H03L7/0814—Details of the phase-locked loop provided with an additional controlled phase shifter and where no voltage or current controlled oscillator is used the phase shifting device being digitally controlled
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K5/00—Manipulating of pulses not covered by one of the other main groups of this subclass
- H03K5/13—Arrangements having a single output and transforming input signals into pulses delivered at desired time intervals
- H03K5/133—Arrangements having a single output and transforming input signals into pulses delivered at desired time intervals using a chain of active delay devices
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/08—Details of the phase-locked loop
- H03L7/081—Details of the phase-locked loop provided with an additional controlled phase shifter
- H03L7/0812—Details of the phase-locked loop provided with an additional controlled phase shifter and where no voltage or current controlled oscillator is used
- H03L7/0816—Details of the phase-locked loop provided with an additional controlled phase shifter and where no voltage or current controlled oscillator is used the controlled phase shifter and the frequency- or phase-detection arrangement being connected to a common input
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/08—Details of the phase-locked loop
- H03L7/085—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal
- H03L7/087—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal using at least two phase detectors or a frequency and phase detector in the loop
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K5/00—Manipulating of pulses not covered by one of the other main groups of this subclass
- H03K2005/00013—Delay, i.e. output pulse is delayed after input pulse and pulse length of output pulse is dependent on pulse length of input pulse
- H03K2005/00019—Variable delay
- H03K2005/00026—Variable delay controlled by an analog electrical signal, e.g. obtained after conversion by a D/A converter
Definitions
- the invention relates to a delay locked loop (DLL) circuit for providing an adjustable phase relationship with respect to a periodic input signal.
- DLL delay locked loop
- DLL circuits are generally used in integrated circuits to derive a clock signal from a reference clock signal with a particular defined phase relationship.
- a conventional DLL circuit (as is used, for example, in integrated circuits) has delay elements which are arranged in a row and form a delay chain.
- a periodic input signal preferably the reference clock signal, is applied to the input of the first delay element in the delay chain.
- the delay time of the delay elements can be adjusted on the basis of an item of control information.
- a phase detector compares the phase relationship of the reference clock signal at the input of the delay chain with that of a signal (which has been phase-shifted with respect to said reference clock signal) at the output of the delay chain, i.e., at the output of the last delay element in the delay chain. If there is a phase difference, an item of control information is generated in order to adjust the delay time of the individual delay elements.
- Such a DLL loop is usually adjusted in such a manner that the delay chain gives rise to a phase shift of 180°, with the result that the delay time or the phase shift of each delay element is given by a phase shift of 180° divided by the number of delay elements in the delay chain.
- the outputs of the delay elements are connected to a selection element which selects one of the outputs of the delay elements on the basis of a selection signal which has been provided and outputs the output from the selected delay element to an output line of the DLL circuit.
- the selection signal corresponds to a desired phase shift of the input signal with respect to a periodic output signal and specifies the number of delay elements through which the reference clock signal is intended to pass between the input line and the output line of the DLL circuit. If phase shifts of between 180° and 360° are required, the selection element can additionally invert the output signal from the relevant delay element in accordance with the selection signal.
- the DLL circuit usually contains further elements which are not compensated for by regulation and which give rise to an additional delay of the reference clock signal, namely an input buffer for the delay chain, which is provided in order to provide the delay chain with an input signal with a defined driver strength, and the selection element, which likewise has a signal delay.
- a phase shift of greater than 0° therefore exists between the periodic input signal and the periodic output signal from the DLL circuit even if a desired phase shift of 0° is selected in the selection element.
- the invention provides a DLL circuit for providing an adjustable phase relationship with respect to a periodic input signal.
- the DLL circuit has controllable delay elements which are connected in series and form a delay chain. Provision is also made of a phase detector which generates a control signal on the basis of the periodic input signal and a periodic signal which has been delayed by the delay chain, the delay of each of the delay elements being adjusted on the basis of the control signal.
- a selection unit which is respectively connected to an output of the delay elements is used to apply an output signal from one of the delay elements to an output of the DLL circuit on the basis of a selection variable which has been provided. Provision is made of a compensation circuit which modifies the selection signal such that an additional delay (which is caused at least by the selection unit) between the periodic input signal and the output signal from the DLL circuit is compensated for.
- the DLL circuit according to the invention makes it possible, by modifying the selection signal, for a desired delay or phase shift of the periodic input signal to be adapted in such a manner that a delay (which is caused by elements other than those in the feedback loop) of the periodic input signal is compensated for.
- This is preferably effected with the aid of a compensation circuit which determines a compensation variable, the compensation circuit also having a modification unit in order to modify the selection variable on the basis of the compensation variable.
- the compensation circuit determines the compensation variable by determining the delay time of at least the selection unit in units of the delay time of the delay elements.
- the compensation circuit has a further selection unit which is connected to the outputs of the delay elements and whose output is connected to a first input of a phase detector.
- the phase detector generates a further control signal on the basis of the periodic input signal and the output signal from a delay element selected by the further selection unit on the basis of the compensation variable, provision being made of a compensation unit which generates the compensation variable on the basis of the further control signal and applies it to the further selection unit in order to select the output signal from one of the delay elements.
- This provides a further feedback loop which adjusts the periodic input signal to a periodic signal which has a phase shift of 0° with respect to the periodic input signal.
- the further feedback loop compensates for the phase shift which results between the periodic input signal and the output signal from the further selection unit by generating a compensation variable.
- the further selection unit it is necessary for the further selection unit to essentially have the same delay time as the selection unit. This is preferably achieved by the selection unit and the further selection unit essentially being of the same physical design.
- the compensation circuit may have a calibration circuit in order to determine the compensation variable in a calibration mode and to provide the modification unit with the compensation variable (which has been determined) in a normal operating mode.
- the calibration circuit has, in particular, a further phase detector which generates a further control signal on the basis of the periodic input signal and the output signal from a delay element which has been selected, using the selection unit, on the basis of the compensation variable, provision being made of a compensation unit which, in the calibration mode, generates the compensation variable on the basis of the further control signal and applies it to the selection unit in order to select the output signal from one of the delay elements.
- the calibration circuit preferably has a memory element.
- FIG. 1 shows a DLL circuit according to the prior art
- FIG. 2 shows a DLL circuit having a calibration circuit according to a first embodiment of the invention
- FIG. 3 shows a DLL circuit having a calibration circuit according to another embodiment of the present invention.
- FIG. 1 illustrates a DLL circuit according to the prior art.
- the DLL circuit is used to shift a periodic input signal (a reference clock signal REFCLK in the present case) in accordance with a prescribed phase shift and to output an output signal A on an output line 1 .
- the DLL circuit may be used, for example, in an integrated circuit in order to apply a clock signal, which is provided at a connection of the integrated circuit, to internal circuits in phase-shifted form or to carry out delay time compensation.
- the DLL circuit has a feedback loop having a delay chain 2 , a phase detector 3 and a loop filter 4 .
- the reference clock signal REFCLK is applied to an input of the delay chain 2 via an input buffer 5 .
- the input buffer 5 is used to apply the periodic input signal with a predetermined driver strength to the input of the delay chain.
- the reference clock signal which is driven through the input buffer 5 is likewise applied to a first input of the phase detector 3 .
- An output of the delay chain 2 is also connected to a second input of the phase detector 3 .
- An output of the phase detector 3 provides a control signal which is connected to an input of the loop filter 4 .
- the delay chain 2 has delay elements 6 which are connected in series, and each delay element has an input, an output and a control input.
- the inputs and outputs of the delay elements 6 are connected in series, and the delay elements each delay the signal which is applied to their input.
- the control inputs of the delay elements are jointly connected to an output of the loop filter 4 , at which the filtered control signal is output from the phase detector 3 .
- the loop filter 4 is essentially used to avoid oscillation of the feedback loop in order to avoid sudden changes by a value which can be adjusted, particularly in the case of delay elements which can be adjusted digitally or discretely.
- the feedback loop formed by the delay chain 2 , the phase detector 3 and the loop filter 4 is adjusted, depending on the phase detector used, in such a manner that the added delay times of each of the delay elements 6 delay the delay chain 2 by 180°. That is to say the signal which is taken from the output of the delay chain 2 and is applied to the second input of the phase detector 3 has been phase-shifted through 180° with respect to the amplified reference clock signal REFCLK.
- the number of delay elements 6 in the delay chain 2 is not restricted to eight, as in the example given; it is expedient to select the number of delay elements to be as large as possible so that the best possible resolution is achieved when selecting the phase shift. Furthermore, depending on the phase detector 3 used, it is also possible to provide a delay chain for a delay of the input signal by 360°, the phase detector 3 determining, in this case, whether the input signal leads or lags the output signal from the delay chain.
- a selection unit 7 which may be in the form of a multiplexer, for example.
- the selection unit 7 has inputs which are directly connected to both the output of the input buffer 5 and the outputs of the individual delay elements in the delay chain 2 .
- the selection unit 7 selects one of the inputs in order to connect it to the output line 1 .
- the delay signal VS is prescribed and thus represents a selection signal for the selection unit 7 in order to select one of the outputs of the delay elements 6 which corresponds to a particular phase shift of the reference clock signal REFCLK.
- the phase shift caused by a delay element can be determined to be 180° divided by the number of delay elements 6 in the delay chain 2 .
- the reference clock signal which has been delayed using none of the delay elements or a particular number of delay elements 6 is now selected and output to the output line 1 as an output signal A.
- a total of eight delay elements 6 are provided for the entire delay chain 2 , with the result that a phase shift of 22.5° results for each of the delay elements.
- the output of the second delay element needs to be connected to the output line 1 via the selection unit 7 , and the delay signal VS needs to be correspondingly selected.
- the selection unit 7 may also have an inverter unit (not shown) in order to invert the signal which has been switched through to the output line 1 , thus making it possible to realize phase shifts of between 180° and 360°. This is preferably likewise prescribed by the delay signal VS.
- FIG. 2 provides a first embodiment of a DLL circuit according to the invention.
- identical reference symbols correspond to elements having identical or comparable functions as those in FIG. 1 .
- the embodiment shown in FIG. 2 has a modification circuit 8 which modifies the delay signal VS in accordance with a compensation signal AS and applies a modified delay signal VS′ to the selection unit 7 .
- a further selection unit 9 which is essentially of the same physical design as the selection unit 7 and has the same signal delay time as the selection unit 7 .
- An output of the further selection unit 9 is connected to a first input of a further phase detector 10 , and a second input of the further phase detector 10 is connected to the reference clock signal REFCLK upstream of the input buffer 5 .
- An output of the further phase detector 10 is connected to a compensation unit 11 which generates the compensation signal AS and provides both the modification circuit 8 and the further selection unit 9 with said compensation signal.
- This compensation signal AS is adjusted, using the feedback loop which is formed by the further phase detector 10 , the compensation unit 11 and the further selection unit 9 , in such a manner that the delay of the further selection unit 9 and of the input buffer 5 is essentially compensated for in units of the adjusted delay times of the delay elements 6 .
- the delay time between the input of the input buffer 5 and the output of the further selection unit 9 said delay time corresponding to the delay time between the input of the input buffer 5 and the output of the selection unit 7 , is determined without the influence of the delay chain 2 and is expressed by the compensation signal AS as a factor of the delay time of a delay element 6 . If, for example, the signal delay which is caused by the input buffer 5 and the further selection unit 9 corresponds to 67.5°, the compensation signal obtained is a compensation variable to the value of “ ⁇ 3”, thus making it possible to compensate for the signal delays of 67.5° using a signal delay of “ ⁇ 67.5°”.
- the modification circuit 8 essentially represents a subtraction circuit in which the compensation signal AS is subtracted from the prescribed delay signal VS in order to obtain the modified delay signal VS′.
- the delay signal VS and the compensation signal AS may represent both digital signals and analog signals in the form of voltages and preferably specify the corresponding delays of the number of delay elements.
- the delay signal VS specifies a value which determines that the output of the fourth delay element 6 in the delay chain 2 is connected to the output line 1 . If the further feedback loop which is formed from the further selection unit 9 , the further phase detector 10 and the compensation unit 11 is used to determine that the phase shift between the input signal and the output signal corresponds to approximately 45° given an assumed set phase shift of 0°, a phase shift of 135° between the input signal and the output signal would result in the DLL circuit according to the prior art since the signal delay times in the selection unit 7 and the input buffer 5 cannot be compensated for by the feedback loop.
- the further feedback loop now determines a compensation signal AS which is calculated in the modification circuit 8 , using the delay signal VS, in such a manner that the number of delay elements through which the input signal passes before it is applied to the output line 1 is reduced, to be precise by a value which corresponds to the phase shift of 45° which is caused by the selection unit 7 and the input buffer 5 .
- the phase shift of 45° may essentially be compensated for using two delay elements 6 , with the result that, in the abovementioned example, the output of the second delay element is connected to the output line 1 instead of the output of the fourth delay element in order to obtain the desired phase shift of 90°.
- FIG. 3 shows an alternative embodiment of the invention.
- identical reference symbols correspond to identical elements having an identical or comparable function as those in FIGS. 1 and 2 .
- the selection unit 7 is used both to output the output signal and to determine the compensation signal AS.
- a calibration circuit which can be operated in two operating modes. In a calibration mode, the phase shift caused by the input buffer 5 and the selection unit 7 is first of all determined and a corresponding compensation variable AS is provided. This compensation variable is stored, and the compensation circuit 8 is provided with said compensation variable in the normal operating mode.
- the output of the selection unit 7 is essentially connected to a first input of a further phase detector 20 .
- a second input of the phase detector 20 is connected to the reference clock signal REFCLK as input signal.
- An output of the phase detector is connected to a compensation unit 21 .
- the compensation unit 21 receives a mode signal MS which specifies whether a calibration mode or a normal operating mode is to be assumed. In the calibration mode, which is indicated by the mode signal MS, the compensation unit 21 determines the compensation variable and stores it in the memory unit 22 .
- the modification circuit 8 is provided with the compensation variable which is stored in the memory unit 22 . Furthermore, a switching device 23 which may be in the form of a multiplexer, for example, provides the modification circuit 8 with a calibration variable in the calibration mode, said calibration variable specifying that the input signal is to be applied, by the delay chain 2 , to the output of the DLL circuit with as little delay as possible, that is to say the output of the input buffer 5 is applied to the output line 1 via the selection unit 7 .
- the delay signal VS which is applied to a second input of the switching device 23 is applied to the modification circuit 8 , with the result that a modified delay signal VS′ is applied to the selection unit 7 on the basis of the delay signal VS and the compensation signal AS.
- the embodiment shown in FIG. 2 essentially differs from the embodiment shown in FIG. 3 by virtue of the fact that, in the last-mentioned embodiment, the further selection element 9 may be dispensed with and, instead, in two operating modes, the compensation variable AS is first of all determined and the compensation variable determined is then used to modify the delay signal in the modification circuit 8 .
- the invention makes it possible, in a DLL circuit, to also take into account the components which are used independently of the feedback loop, such as the selection unit 7 (multiplexer) and the input buffer 5 which is connected upstream of the feedback loop, with the result that the phase shift between the periodic input signal and the phase-shifted output signal can be exactly adjusted to the value specified by the delay signal VS.
Abstract
Description
- This application claims foreign priority benefits under 35 U.S.C. §119 to co-pending German patent
application number DE 10 2005 008 151.7, filed 23 Feb. 2005. This related patent application is herein incorporated by reference in its entirety. - 1. Field of the Invention
- The invention relates to a delay locked loop (DLL) circuit for providing an adjustable phase relationship with respect to a periodic input signal.
- 2. Description of the Related Art
- DLL circuits are generally used in integrated circuits to derive a clock signal from a reference clock signal with a particular defined phase relationship. A conventional DLL circuit (as is used, for example, in integrated circuits) has delay elements which are arranged in a row and form a delay chain. A periodic input signal, preferably the reference clock signal, is applied to the input of the first delay element in the delay chain. The delay time of the delay elements can be adjusted on the basis of an item of control information. A phase detector compares the phase relationship of the reference clock signal at the input of the delay chain with that of a signal (which has been phase-shifted with respect to said reference clock signal) at the output of the delay chain, i.e., at the output of the last delay element in the delay chain. If there is a phase difference, an item of control information is generated in order to adjust the delay time of the individual delay elements.
- Such a DLL loop is usually adjusted in such a manner that the delay chain gives rise to a phase shift of 180°, with the result that the delay time or the phase shift of each delay element is given by a phase shift of 180° divided by the number of delay elements in the delay chain. The outputs of the delay elements are connected to a selection element which selects one of the outputs of the delay elements on the basis of a selection signal which has been provided and outputs the output from the selected delay element to an output line of the DLL circuit. The selection signal corresponds to a desired phase shift of the input signal with respect to a periodic output signal and specifies the number of delay elements through which the reference clock signal is intended to pass between the input line and the output line of the DLL circuit. If phase shifts of between 180° and 360° are required, the selection element can additionally invert the output signal from the relevant delay element in accordance with the selection signal.
- On account of the regulation of the feedback loop, all variations in the process parameters, the operating voltage or the temperature which influence the delay time of the delay elements, insofar as they influence the phase shift of the entire delay chain, are compensated for. However, the DLL circuit usually contains further elements which are not compensated for by regulation and which give rise to an additional delay of the reference clock signal, namely an input buffer for the delay chain, which is provided in order to provide the delay chain with an input signal with a defined driver strength, and the selection element, which likewise has a signal delay. A phase shift of greater than 0° therefore exists between the periodic input signal and the periodic output signal from the DLL circuit even if a desired phase shift of 0° is selected in the selection element.
- It is an object of the present invention to provide a DLL circuit in which compensates for the influence of elements (which are not arranged in the feedback circuit) on the phase shift.
- The invention provides a DLL circuit for providing an adjustable phase relationship with respect to a periodic input signal. The DLL circuit has controllable delay elements which are connected in series and form a delay chain. Provision is also made of a phase detector which generates a control signal on the basis of the periodic input signal and a periodic signal which has been delayed by the delay chain, the delay of each of the delay elements being adjusted on the basis of the control signal. A selection unit which is respectively connected to an output of the delay elements is used to apply an output signal from one of the delay elements to an output of the DLL circuit on the basis of a selection variable which has been provided. Provision is made of a compensation circuit which modifies the selection signal such that an additional delay (which is caused at least by the selection unit) between the periodic input signal and the output signal from the DLL circuit is compensated for.
- The DLL circuit according to the invention makes it possible, by modifying the selection signal, for a desired delay or phase shift of the periodic input signal to be adapted in such a manner that a delay (which is caused by elements other than those in the feedback loop) of the periodic input signal is compensated for.
- This is preferably effected with the aid of a compensation circuit which determines a compensation variable, the compensation circuit also having a modification unit in order to modify the selection variable on the basis of the compensation variable.
- In particular, the compensation circuit determines the compensation variable by determining the delay time of at least the selection unit in units of the delay time of the delay elements.
- In accordance with one preferred embodiment, the compensation circuit has a further selection unit which is connected to the outputs of the delay elements and whose output is connected to a first input of a phase detector. The phase detector generates a further control signal on the basis of the periodic input signal and the output signal from a delay element selected by the further selection unit on the basis of the compensation variable, provision being made of a compensation unit which generates the compensation variable on the basis of the further control signal and applies it to the further selection unit in order to select the output signal from one of the delay elements. This provides a further feedback loop which adjusts the periodic input signal to a periodic signal which has a phase shift of 0° with respect to the periodic input signal. The further feedback loop compensates for the phase shift which results between the periodic input signal and the output signal from the further selection unit by generating a compensation variable. To this end, it is necessary for the further selection unit to essentially have the same delay time as the selection unit. This is preferably achieved by the selection unit and the further selection unit essentially being of the same physical design.
- In accordance with another embodiment of the present invention, the compensation circuit may have a calibration circuit in order to determine the compensation variable in a calibration mode and to provide the modification unit with the compensation variable (which has been determined) in a normal operating mode. To this end, the calibration circuit has, in particular, a further phase detector which generates a further control signal on the basis of the periodic input signal and the output signal from a delay element which has been selected, using the selection unit, on the basis of the compensation variable, provision being made of a compensation unit which, in the calibration mode, generates the compensation variable on the basis of the further control signal and applies it to the selection unit in order to select the output signal from one of the delay elements.
- In order to provide the modification unit with the compensation variable (which has been determined) in the normal operating mode, the calibration circuit preferably has a memory element.
- Provision may also be made of a selection switch which, in the normal operating mode, provides the modification unit with the selection variable on the basis of a calibration mode signal and, in the calibration mode, applies a selection variable to the modification unit, said variable having a value which corresponds to no delay by the delay elements.
- So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
-
FIG. 1 shows a DLL circuit according to the prior art; -
FIG. 2 shows a DLL circuit having a calibration circuit according to a first embodiment of the invention; and -
FIG. 3 shows a DLL circuit having a calibration circuit according to another embodiment of the present invention. -
FIG. 1 illustrates a DLL circuit according to the prior art. The DLL circuit is used to shift a periodic input signal (a reference clock signal REFCLK in the present case) in accordance with a prescribed phase shift and to output an output signal A on anoutput line 1. The DLL circuit may be used, for example, in an integrated circuit in order to apply a clock signal, which is provided at a connection of the integrated circuit, to internal circuits in phase-shifted form or to carry out delay time compensation. - The DLL circuit has a feedback loop having a
delay chain 2, aphase detector 3 and aloop filter 4. The reference clock signal REFCLK is applied to an input of thedelay chain 2 via aninput buffer 5. Theinput buffer 5 is used to apply the periodic input signal with a predetermined driver strength to the input of the delay chain. The reference clock signal which is driven through theinput buffer 5 is likewise applied to a first input of thephase detector 3. An output of thedelay chain 2 is also connected to a second input of thephase detector 3. An output of thephase detector 3 provides a control signal which is connected to an input of theloop filter 4. - The
delay chain 2 hasdelay elements 6 which are connected in series, and each delay element has an input, an output and a control input. The inputs and outputs of thedelay elements 6 are connected in series, and the delay elements each delay the signal which is applied to their input. The control inputs of the delay elements are jointly connected to an output of theloop filter 4, at which the filtered control signal is output from thephase detector 3. - The
loop filter 4 is essentially used to avoid oscillation of the feedback loop in order to avoid sudden changes by a value which can be adjusted, particularly in the case of delay elements which can be adjusted digitally or discretely. - The feedback loop formed by the
delay chain 2, thephase detector 3 and theloop filter 4 is adjusted, depending on the phase detector used, in such a manner that the added delay times of each of thedelay elements 6 delay thedelay chain 2 by 180°. That is to say the signal which is taken from the output of thedelay chain 2 and is applied to the second input of thephase detector 3 has been phase-shifted through 180° with respect to the amplified reference clock signal REFCLK. - The number of
delay elements 6 in thedelay chain 2 is not restricted to eight, as in the example given; it is expedient to select the number of delay elements to be as large as possible so that the best possible resolution is achieved when selecting the phase shift. Furthermore, depending on thephase detector 3 used, it is also possible to provide a delay chain for a delay of the input signal by 360°, thephase detector 3 determining, in this case, whether the input signal leads or lags the output signal from the delay chain. - Provision is also made of a
selection unit 7 which may be in the form of a multiplexer, for example. Theselection unit 7 has inputs which are directly connected to both the output of theinput buffer 5 and the outputs of the individual delay elements in thedelay chain 2. In accordance with a delay signal VS which specifies the desired phase shift, theselection unit 7 selects one of the inputs in order to connect it to theoutput line 1. The delay signal VS is prescribed and thus represents a selection signal for theselection unit 7 in order to select one of the outputs of thedelay elements 6 which corresponds to a particular phase shift of the reference clock signal REFCLK. Since the number ofdelay elements 6 in thedelay chain 2 is known, and it is also known that, in the steady state, the feedback loop adjusts the delay of thedelay chain 2 to a phase shift of exactly 180°, the phase shift caused by a delay element can be determined to be 180° divided by the number ofdelay elements 6 in thedelay chain 2. In accordance with the delay signal VS, the reference clock signal which has been delayed using none of the delay elements or a particular number ofdelay elements 6 is now selected and output to theoutput line 1 as an output signal A. In the present example, a total of eightdelay elements 6 are provided for theentire delay chain 2, with the result that a phase shift of 22.5° results for each of the delay elements. If a phase shift of 45° is to be achieved between the reference clock signal REFCLK and the output signal A, the output of the second delay element needs to be connected to theoutput line 1 via theselection unit 7, and the delay signal VS needs to be correspondingly selected. Theselection unit 7 may also have an inverter unit (not shown) in order to invert the signal which has been switched through to theoutput line 1, thus making it possible to realize phase shifts of between 180° and 360°. This is preferably likewise prescribed by the delay signal VS. - Whereas process-dictated influences on the delay time of the delay elements and influences which are dependent on the supply voltage and on the temperature are compensated for in the feedback loop, the signal delays within the
selection unit 7 and within theinput buffer 5 are not compensated for by the feedback loop. A corresponding additional signal delay which is given by the signal delays of theselection unit 7 and of theinput buffer 5 is thus always applied to the phase shift between the periodic input signal of the DLL circuit and the output signal from the DLL circuit. Since this may result in different additional phase shifts in the case of a variable frequency of the periodic input signal, it is desirable to minimize or eliminate these influences as far as possible. - To this end,
FIG. 2 provides a first embodiment of a DLL circuit according to the invention. In that figure, identical reference symbols correspond to elements having identical or comparable functions as those inFIG. 1 . - In order to compensate for the phase shift which is caused by the
selection unit 7 and theinput buffer 5, the embodiment shown inFIG. 2 has amodification circuit 8 which modifies the delay signal VS in accordance with a compensation signal AS and applies a modified delay signal VS′ to theselection unit 7. To this end, provision is made of afurther selection unit 9 which is essentially of the same physical design as theselection unit 7 and has the same signal delay time as theselection unit 7. An output of thefurther selection unit 9 is connected to a first input of afurther phase detector 10, and a second input of thefurther phase detector 10 is connected to the reference clock signal REFCLK upstream of theinput buffer 5. An output of thefurther phase detector 10 is connected to acompensation unit 11 which generates the compensation signal AS and provides both themodification circuit 8 and thefurther selection unit 9 with said compensation signal. This compensation signal AS is adjusted, using the feedback loop which is formed by thefurther phase detector 10, thecompensation unit 11 and thefurther selection unit 9, in such a manner that the delay of thefurther selection unit 9 and of theinput buffer 5 is essentially compensated for in units of the adjusted delay times of thedelay elements 6. That is to say the delay time between the input of theinput buffer 5 and the output of thefurther selection unit 9, said delay time corresponding to the delay time between the input of theinput buffer 5 and the output of theselection unit 7, is determined without the influence of thedelay chain 2 and is expressed by the compensation signal AS as a factor of the delay time of adelay element 6. If, for example, the signal delay which is caused by theinput buffer 5 and thefurther selection unit 9 corresponds to 67.5°, the compensation signal obtained is a compensation variable to the value of “−3”, thus making it possible to compensate for the signal delays of 67.5° using a signal delay of “−67.5°”. In the exemplary embodiment illustrated, themodification circuit 8 essentially represents a subtraction circuit in which the compensation signal AS is subtracted from the prescribed delay signal VS in order to obtain the modified delay signal VS′. The delay signal VS and the compensation signal AS may represent both digital signals and analog signals in the form of voltages and preferably specify the corresponding delays of the number of delay elements. - If, for example, a phase shift of 90° is to be achieved between the input signal and the output signal in the DLL circuit, the delay signal VS, in the exemplary embodiment illustrated in
FIG. 2 , specifies a value which determines that the output of thefourth delay element 6 in thedelay chain 2 is connected to theoutput line 1. If the further feedback loop which is formed from thefurther selection unit 9, thefurther phase detector 10 and thecompensation unit 11 is used to determine that the phase shift between the input signal and the output signal corresponds to approximately 45° given an assumed set phase shift of 0°, a phase shift of 135° between the input signal and the output signal would result in the DLL circuit according to the prior art since the signal delay times in theselection unit 7 and theinput buffer 5 cannot be compensated for by the feedback loop. The further feedback loop now determines a compensation signal AS which is calculated in themodification circuit 8, using the delay signal VS, in such a manner that the number of delay elements through which the input signal passes before it is applied to theoutput line 1 is reduced, to be precise by a value which corresponds to the phase shift of 45° which is caused by theselection unit 7 and theinput buffer 5. The phase shift of 45° may essentially be compensated for using twodelay elements 6, with the result that, in the abovementioned example, the output of the second delay element is connected to theoutput line 1 instead of the output of the fourth delay element in order to obtain the desired phase shift of 90°. -
FIG. 3 shows an alternative embodiment of the invention. In this case too, identical reference symbols correspond to identical elements having an identical or comparable function as those inFIGS. 1 and 2 . Instead of a further selection unit, theselection unit 7 is used both to output the output signal and to determine the compensation signal AS. To this end, use is made of a calibration circuit which can be operated in two operating modes. In a calibration mode, the phase shift caused by theinput buffer 5 and theselection unit 7 is first of all determined and a corresponding compensation variable AS is provided. This compensation variable is stored, and thecompensation circuit 8 is provided with said compensation variable in the normal operating mode. To this end, the output of theselection unit 7 is essentially connected to a first input of afurther phase detector 20. A second input of thephase detector 20 is connected to the reference clock signal REFCLK as input signal. An output of the phase detector is connected to acompensation unit 21. Thecompensation unit 21 receives a mode signal MS which specifies whether a calibration mode or a normal operating mode is to be assumed. In the calibration mode, which is indicated by the mode signal MS, thecompensation unit 21 determines the compensation variable and stores it in thememory unit 22. - If the mode signal MS indicates the normal operating mode, the
modification circuit 8 is provided with the compensation variable which is stored in thememory unit 22. Furthermore, aswitching device 23 which may be in the form of a multiplexer, for example, provides themodification circuit 8 with a calibration variable in the calibration mode, said calibration variable specifying that the input signal is to be applied, by thedelay chain 2, to the output of the DLL circuit with as little delay as possible, that is to say the output of theinput buffer 5 is applied to theoutput line 1 via theselection unit 7. In the normal operating mode, the delay signal VS which is applied to a second input of theswitching device 23 is applied to themodification circuit 8, with the result that a modified delay signal VS′ is applied to theselection unit 7 on the basis of the delay signal VS and the compensation signal AS. - The embodiment shown in
FIG. 2 essentially differs from the embodiment shown inFIG. 3 by virtue of the fact that, in the last-mentioned embodiment, thefurther selection element 9 may be dispensed with and, instead, in two operating modes, the compensation variable AS is first of all determined and the compensation variable determined is then used to modify the delay signal in themodification circuit 8. - The invention makes it possible, in a DLL circuit, to also take into account the components which are used independently of the feedback loop, such as the selection unit 7 (multiplexer) and the
input buffer 5 which is connected upstream of the feedback loop, with the result that the phase shift between the periodic input signal and the phase-shifted output signal can be exactly adjusted to the value specified by the delay signal VS. - The features of the various embodiments may be combined with one another in any desired manner—provided that they do not technically exclude one another in an obvious manner—without departing from the field of the present invention.
- While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
Claims (20)
Applications Claiming Priority (2)
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DEDE102005008151.7 | 2005-02-23 | ||
DE102005008151A DE102005008151B4 (en) | 2005-02-23 | 2005-02-23 | DLL circuit for providing an adjustable phase relationship to a periodic input signal |
Publications (2)
Publication Number | Publication Date |
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US20060197567A1 true US20060197567A1 (en) | 2006-09-07 |
US7339407B2 US7339407B2 (en) | 2008-03-04 |
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Family Applications (1)
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US11/360,988 Expired - Fee Related US7339407B2 (en) | 2005-02-23 | 2006-02-23 | DLL circuit for providing an adjustable phase relationship with respect to a periodic input signal |
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US (1) | US7339407B2 (en) |
CN (1) | CN1825768B (en) |
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US20100052651A1 (en) * | 2008-08-28 | 2010-03-04 | Advantest Corporation | Pulse width measurement circuit |
US7737742B2 (en) | 2008-02-14 | 2010-06-15 | Qimonda Ag | Delay locked loop |
CN103259535A (en) * | 2012-02-15 | 2013-08-21 | 联咏科技股份有限公司 | Delay phase locking return circuit and delay phase locking method |
US8705654B1 (en) * | 2009-10-08 | 2014-04-22 | Rf Micro Devices, Inc. | Measuring phase shift in a radio frequency power amplifier |
US8909065B2 (en) | 2011-07-15 | 2014-12-09 | Intel Mobile Communications GmbH | Adjustable delayer, method for delaying an input signal and polar transmitter |
WO2018233675A1 (en) * | 2017-06-22 | 2018-12-27 | Huawei Technologies Co., Ltd. | Methods and apparatus of adjusting delays of signals |
US10254783B2 (en) | 2017-06-28 | 2019-04-09 | Western Digital Technologies, Inc. | External clock based clock generator |
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TWI330945B (en) * | 2006-07-06 | 2010-09-21 | Sunplus Technology Co Ltd | Delay control circuit |
TWI331453B (en) * | 2007-01-17 | 2010-10-01 | Nanya Technology Corp | Delay locked loop |
US7646227B2 (en) * | 2007-07-20 | 2010-01-12 | Taiwan Semiconductor Manufacturing Co., Ltd. | Digital phase discriminator |
US7816960B2 (en) * | 2007-08-09 | 2010-10-19 | Qualcomm Incorporated | Circuit device and method of measuring clock jitter |
DE102009030039A1 (en) * | 2009-06-23 | 2010-12-30 | Rohde & Schwarz Gmbh & Co. Kg | Device for generating a predetermined phase shift |
CN103441757B (en) * | 2013-08-28 | 2016-02-10 | 龙芯中科技术有限公司 | Leggy delay phase-locked loop and control method thereof |
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Also Published As
Publication number | Publication date |
---|---|
CN1825768B (en) | 2012-07-18 |
US7339407B2 (en) | 2008-03-04 |
CN1825768A (en) | 2006-08-30 |
DE102005008151B4 (en) | 2008-02-28 |
DE102005008151A1 (en) | 2006-08-24 |
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